Showing papers on "Microphone published in 1989"

Directional sensitivity of sound‐pressure levels in the human ear canal

Abstract: Changes in sound pressures measured in the ear canal are reported for broadband sound sources positioned at various locations about the subject. These location-dependent pressures are one source of acoustical cues for sound localization by human listeners. Sound source locations were tested with horizontal and vertical resolution of 10 degrees. Sound levels were measured with miniature microphones placed inside the two ear canals. Although the measured amplitude spectra varied with the position of the microphone in the ear canal, it is shown that the directional sensitivity at any particular frequency of the broadband stimulus is independent of microphone position anywhere within the ear canal. At any given frequency, the distribution of sound pressures as a function of sound source location formed a characteristic spatial pattern comprising one or two discrete areas from which sound sources produced maximum levels in the ear canal. The locations of these discrete areas varied in horizontal and vertical location according to sound frequency. For example, around 8 kHz, two areas of maximum sensitivity typically were found that were located laterally and were separated from each other vertically, whereas, around 12 kHz, two such areas were found located on the horizontal plane and separated horizontally. The spatial patterns of sound levels were remarkably similar among different subjects, although some frequency scaling was required to accommodate for differences in the subjects' physical sizes. Interaural differences in sound-pressure level (ILDs) at frequencies below about 8 kHz tended to increase monotonically with increasing distance of the sound source from the frontal midline and tended to be relatively constant as a function of vertical source location. At higher frequencies, however, ILDs varied both with the horizontal and with the vertical location of the sound source. At some frequencies, asymmetries between the left and right ears in a given subject resulted in substantial ILDs even for midline sound sources. These results indicate the types of horizontal and vertical spatial information that are available from sound level cues over various ranges of frequency and, within a small subject population, indicate the nature of intersubject variability.

Active noise reduction system

Abstract: An electro-acoustical feedback system (Fig. 6) which actively and passively attenuates ambient noise, uses shunt control network (60) for compensation. This network comprises several filters (61, 62, 63) parallel with the acoustical path (T16). The shunt control network dominates the loop response at low and at high frequency extremes and so stabilizes the feedback performance. A secondary feedback loop (59 and Fig. 4) is used in conjunction with a bilateral transducer (MT2) to reduce the effect of speaker diaphragm resonance and to modify in other ways the phase and amplitude response of the speaker. A bilateral transducer (MT2) serves simultaneously as a speaker to generate sound and as a microphone to sense sound in a controlled volume. An in-the-ear implementation of the electro-acoustical feedback system (Fig. 2) is shown. Forward acoustical seal is made between earplug flange (38) and the wall (42) of the ear canal (36). This isolates a small controlled volume aiding active and passive attenuation. The application of the in-the-ear active noise reduction is in hearing protection, with or without communication capability. The improvement in intelligibility in noisy environment makes this type of device attractive for vehicular communication and in noisy industrial locations. Specialized applications include electronic stethoscopes and hearing aids.

Intercom apparatus for integrating disparate audio sources for use in light aircraft or similar high noise environments

Abstract: Intercom apparatus having stereo amplifiers adapted for connection to one or more headsets. A plurality of headset output and microphone input connections are provided. Each microphone input includes a separate microphone switch and audio detector whereby only microphone inputs having voice audio thereon are activated. Stereo entertainment and aircraft radio audio inputs are provided. An aircraft radio audio detector is interfaced, along with the various microphone audio detectors, to entertainment partial mute circuitry whereby the presence of a voice or radio audio signal lowers the amplitude of the entertainment input. Microphone and aircraft radio partial mute circuitry are interfaced through a priority selector switch with respective microphone and radio signal detectors. The priority selector switch is a two position, center off arrangement whereby, in one position, aircraft radio signals partially mute microphone signals and in the second position microphone signals partially mute aircraft radio signals. In the center off position no cross muting occurs and the respective signals sum in conventional manner.

Electroacoustic device for hearing needs including noise cancellation

Abstract: A device for performing electroacoustic functions including noise cancellation, hearing aid, communication interface, headset, feed for recording device, and headphone functions. The device includes composite transducers connected to a control unit. The composite transducers can be mounted on a headband and are configured to include input transducers for converting acoustic waves into electrical signals for processing by a control unit, and output transducers for converting the processed electrical signals to processed sound waves. The control unit includes an inverter/amplifier and a mixer/output amplifier for inverting the electrical input and controlling the gain for either adjusting the gain to maximize a noise cancellation function or increasing the gain beyond the minimum level heard by the ear to a desired level for a hearing aid function. Connectors for connecting recorders and a boom microphone, and function selection switches are provided by the control means for connecting circuit components of the control unit selectively for performing the above functions. The input and output transducers have oppositely oriented diaphragms mounted in a common plane to provide an inverted acoustic wave in real time for combining with and substantially cancelling an incoming acoustic wave. 1

Loudspeaking telephone station including directional microphone

Abstract: A loudspeaking telephone station (speakerphone) includes a loudspeaker and one or more microphones within the same housing. The microphones are directional, each having a polar response characteristic that includes a major lobe, one or more side lobes, and nulls between pairs of lobes. The loudspeaker is positioned in the null of the polar response characteristic that resides between the major lobe and an adjacent side lobe. The microphone apparatus is positioned so that its major lobe is aimed in a direction that is generally perpendicular to the direction that the loudspeaker is aimed. Means are provided for increasing the distance between input sound ports of a first-order-gradient (FOG) microphone and thereby improving its sensitivity. A pair of such improved FOG microphones are used in assembling a second-order-gradient microphone. Full duplex operation is achieved when a pair of echo cancelers are added to further reduce the coupling between the transmit and receive directions of the speakerphone.

Clinical evaluation of semiautomatic and automatic devices for home blood pressure measurement: comparison between cuff-oscillometric and microphone methods.

Abstract: The accuracy and reliability of blood pressure (BP) values were evaluated by comparing values obtained with eight automatic or semiautomatic devices designed for home BP measurement (four microphone devices based on the Korotkoff-sound technique and four cuff-oscillometric devices) with those obtain

Measurement of spatial information in sound fields by closely located four point microphone method.

Abstract: When we estimate a sound field in a room, it is important to grasp the spatial informa-tion, especially of the early reflection periods. In this paper we'll discuss a way to grasp the spatial information of sound fields from impulse responses measured at closely located four points, the origin and three points of the same distance (3∼5cm) from the origin on the rectangular coordinate axes. From these four impulse responses the coordinates and powers of virtual image sources are calculated by correlation technique or intensity technique. Concert halls, opera theaters and many other sound fields are measured by this technique. The distributions of virtual image sources and directivity patterns of some concert halls are shown.

Speech communication system and method

Abstract: An electronic system and method for communicating and composing messages by means of speech spoken into a microphone (11). Speech signals output by a microphone when select words of speech are spoken therein, are computer processed and analyzed by a computer (19) to generate select code signals. The body of a message is formed either of such code signals generated when select speech is spoken and computer an­alyzed or when the results of such analysis, select code signals, are employed to query a memory in which a plurality of messages are stored, to selectively reproduce a message or messages therefrom to comprise the information or message desired to be transmitted. The identity of the sender or message composer and one or more recipients of the message or messages so formed, are functions also effected by the computer analysis of speech signals generated when select words of speech are spoken into the microphone. Routing instructions or switching codes for the message are also generated as a result of speaking select speech into the microphone, either by computer anal­ysis of each word or group of words spoken to generate codes defining the switching codes or by employing codes to generated to query a memory to generate the switching signals and incorporate same in a series of code signals defining the message to be transmitted, the identity of the sender and recipient(s) and such switching code signals. In a modified form of the invention, all or part of the body of a message is formed of digitized analog speech signals gen­erated when words of speech defining the message are spoken into a microphone is sequence with other words of speech defining the re­cipient of the message and routing instructions or switching sig­nals. Other functions relating to the message or messages so gener­ated may also be controlled by computer analysis of speech signals defining select control commands.

Active acoustic attenuation system for higher order mode non-uniform sound field in a duct

Abstract: A system is provided for increasing the frequency range of an active acoustic attenuation system in a duct without increasing cut-off frequency fc of the duct or otherwise splitting or partitioning the duct into separate ducts or chambers. The frequency range is increased above fc to include higher order modes. A plurality of cancelling model sets are provided. Each transverse portion of the acoustic pressure wave has its own set of an adaptive filter model, cancelling speaker, and error microphone. A single input microphone may service all sets.

Portable communication device

Abstract: A portable radio device in which a radio telephone device body and a receiver unit are separately constructed and connected together by a pair of adjustable supporting rods As a result, the distance between the radio telephone device body and the receiver unit can be adjusted according to whether the device is being used as a telephone unit or a pager unit While being used as a telephone, the distance between a receiver and a microphone can be easily adjusted to the distance between an ear and a mouth of a user When the device is used as a pager, it can be miniaturized so as to be conveniently carried

Active noise control

Abstract: An active noise control system for controlling noise propagated through a duct comprises a first microphone located to receive the propagated noise at a point in a plane perpendicular to the length of the duct. A loudspeaker is located substantially at that plane for introducing sound into the duct. An analog first control circuit is operative in response to the noise received by the first microphone to feed a signal to the loudspeaker such that the sound introduced thereby destructively interferes with the noise at that point. A second microphone is located further downstream to receive residual noise propagated along the duct despite the destructive interference. A second control circuit, responsive to the residual noise received by the second microphone, controls parameters of the analog first control circuit so as to minimize the residual noise. In particular, the first control circuit includes an integrator which has a transfer function which is electrically controlled by the second control circuit.

Talk/listen headset

Abstract: In a talk/listen headset, essentially comprising two ear protection capsules (1, 2) connected to one another via a headband (3), two microphones (6, 7) are located in one of these along a vertical (9) which runs, projected on the head of the wearer, through the middle of the temporal bone and extends up to the mandibular angle. While the upper microphone (6) acts in the area of the end of the zygomatic arch, the lower microphone (7) is located in the area of the articular process of the ascending ramus of the jaw. Both microphones (6, 7) react to solid-borne sound and are piezoelectric resonators with a mass-forming body, an impedance converter and a filter/equalizer, the microphones being connected to one another in terms of voltage in order to absorb or compensate the local tone amplitudes to the bottom and to the top caused by the reproduction. This has the effect that this indirect reproduction of the voice is optimised in terms of tone and timbre. The ear protection capsules (1, 2) also contain earphones (4a, 4b) and one receiving element (12a, 12b) each. The latter are directed towards the background noises. Microphones (6, 7), earphones (4a, 4b) and receiving elements (12a, 12b) interact with an electronic component (13) integrated in the ear protection capsules, the circuit of which component has, inter alia a communication priority in favor of the microphones and earphones and not in favor of the receiving elements.

Electret condenser microphone

Abstract: An electret condenser microphone includes a cup-­shaped metallic case (11) having an apertured end wall (11a), a tubular metal ring (12) received in the metallic case (11), a vibratory diaphragm (13) having on its one surface a deposited metal film (13a) and bonded to an end face of the tubular metal ring (12) in confronting relation to the end wall (11a) with an air gap (19) defined therebe­tween, and a condenser composed of a movable electrode and a fixed counter electrode, the fixed counter electrode com­prising at least a part of the end wall (11a) of the metal­lic case (11) while the movable electrode comprises the vibratory diaphragm (13) Partly because the end wall (11a) of the metallic case (11) serves as the fixed electrode, and partly because the vibratory diaphragm (13) is bonded to the end face of the metal ring (12), the number of the compo­nents of the microphone is relatively small With this small number of components, the microphone is simple in construction and can be manufactured at a low cost, and further has a relatively large rear cavity (14) behind the vibratory diaphragm (13), which improves the sensitivity of the microphone

Automatic calibrating apparatus and method for second-order gradient microphone

Abstract: An automatic calibration system for a second-order gradient microphone is provided to ensure optimum sensitivity balance between a pair of first-order gradient microphones mounted in a housing and forming the second-order gradient microphone. Automatic calibration is achieved through use of a transducer also mounted in the housing and located equidistant acoustically between the two first-order gradient microphones. Under the control of a computer, the transducer is directed to generated sound pressure which is used to calibrate the gain of amplifiers respectively associated with each one of the first-order gradient microphones for obtaining maximum directional sensitivity for a second-order directional response pattern. Such a system not only allows the use of inexpensive, non-matched microphones, but also obviates the need for factory calibration. Since the system is configurable to optimize itself automatically prior to use, calibration may be maintained regardless of aging, environmental stresses and parts replacement.

Integrated microphone with CMOS circuits on a single chip

Abstract: Summary form only given. The first integration of a microphone together with CMOS circuits on a single chip has been demonstrated. It was found that the processes needed to make the microphone can be articulated with a commercial CMOS fabrication line. The microphones, squares 2 mm on a side, were fabricated by combining micromachining procedures (to produce a thin silicon-nitride diaphragm) with ZnO thin-film layers which are used as piezoelectric transducers. The circuits integrated with the microphones consist mainly of several configurations of analog standard cells that were designed and proven for building-block applications. The frequency responses of the integrated microphones are plotted. >

Sound level control equipment

Abstract: Automatic level control equipment, for example for a coin-operated music system, has a sound level adjusting device, such as a variable resistance device (30) interposed between amplifier inputs (23) and outputs (24) for sound reproducing apparatus, such as loudspeakers. The resistance (30) is adjusted by control circuitry (28) to compensate for changes in the level of background noise picked up by a microphone (22). The control circuitry (28) has microphone monitoring filters (25) and amplifier output monitoring filters (27) operable at different frequency bands so that background noise can be monitored at different frequency bands, depending on the frequency distribution of the sound output of the amplifier. If the amplifier has a sound output in the same frequency band as that being monitored in the background noise, the circuitry can switch to a different monitored frequency band of background noise.

Hearing aid with transmitter and microphone housing parts

Abstract: A hearing aid is described comprising a transmitter housing part and a microphone housing part associated with the external ear, together with associated actuating units and is characterized in that the microphone housing part is formed as a plastic hook or an at least partially elastically deformable unit adaptable individually to the curve of the concha, and in that the microphone is arranged in the end region remote from the transmitter housing part

Subminiature silicon integrated electret capacitor microphone

Abstract: Microphones were prepared that use one silicon wafer to support a thin polyester diaphragm and a second to carry a Teflon or silicon dioxide electret. Subassemblies are diced from the wafer and bonded together to form complete microphones. The preamplifier circuit can be carried on either subassembly. Microphones with reasonable signal-to-noise ratios can be obtained with edge dimensions of 3 mm or less. The electroacoustic properties of prototype units are described. >

Acoustic leak detection system

Abstract: Paper pulp mill chemical recovery boiler steam piping is monitored for leaks by an acoustic leak detection system responsive to atmospherically carried sound transmissions. Energy level amplitudes of respective analog electrical signals generated by a multiplicity of microphones are digitized in a rapid time sequence. Such digital values are temporarily stored in a data memory bank to be subsequently processed by a Fast-Fourier Transform analysis into amplitude vs. frequency domain data. Such amplitude vs. frequency data respective to each microphone is further refined for comparison to historical threshold data for a probability determination of a leak status.

Electronic animal repellant apparatus

Abstract: An electronic animal repellant apparatus includes a microphone for detecting environmental sound, a detection circuit for detecting the presence of a particular species of animal in the vicinity of the repellant apparatus, a timing and activation circuit, and a plurality of animal repellant or frightening devices. The microphone produces an input signal fed to the detection circuit that has a frequency content representative of the frequency spectrum of the environmental sound. The input signal is compared to a pre-determined frequency envelope characteristic of the sound spectrum of the particular animal species and a trigger signal is produced when the presence of the particular animal is detected. The detection circuit includes a band-pass filter and a negative feedback band-reject filter, each having readily removable and replaceable components for changing the pre-determined frequency envelope for different species of animal to be repelled. The trigger signal is provided to the timing and activation circuit which provides signals to activate one or more of the plurality of animal frightening devices. The timing and activation circuit includes circuitry to provide a random delay in activation of the frightening device, a random duration of activation, and a random sequence of activation of more than one of the plurality of devices.

Hearing aid transducer

Abstract: This invention is concerned with a hearing aid including a microphone, an adjustable amplifier, and an acoustic transducer positioned within a first, large acoustic chamber defined by an in-the-ear housing. The acoustic transducer is in communication with a sound outlet passage which leads into the user's ear canal. The acoustic transducer includes a sound generating diaphragm driven by an acoustic driver. The diaphragm and driver are mounted in the acoustic transducer, with the diaphragm dividing the transducer into second and third acoustic chambers. A vent passage is provided between the first and third acoustic chambers. An acoustic resistance is mounted in the vent passage to modify the operating characteristics of the hearing aid.

Bladder device for monitoring pulse and respiration rate

Abstract: A medical monitoring device monitors the pulse and respiration rate of an infant, and transmits an alarm signal to a remote receiver when pulse and/or respiration rate irregularities are detected The device incorporates an acoustic sensor (microphone) and pressure sensor adjacent a small gas or liquid-filled bag or bladder member The bladder member and attached sensors are contained in a compact monitor housing which is positioned against the monitored infant's body, so that the bladder member directly contacts the body, and is preferably held in place by a small belt wrapped around the infant

Adaptive array processing for multiple microphone hearing aids

Abstract: Hearing-aid users often have difficulty functioning in acoustic environments with many sound sources and/or substantial reverberation. It may be possible to improve hearing aids (and other sensory aids, such as cochlear implants or tactile aids for the deaf) by using multiple microphones to distinguish between spatially-separate sources of sound in a room. This thesis examines adaptive beamforming as one method for combining the signals from an array of head-mounted microphones to form one signal in which a particular sound source is emphasized relative to all other sources. In theoretical work, bounds on the performance of adaptive beamformers are calculated for head-sized line arrays in stationary, anechoic environments with isotropic and multiple-discrete-source interference. Substantial performance gains relative to a single microphone or to conventional, non-adaptive beamforming are possible, depending on the interference, allowable sensitivity to sensor noise, array orientation, and number of microphones. Endfire orientations often outperform broadside orientations and using more that about 5 microphones in a line array does not improve performance. In experimental work, the intelligibility of target speech is measured for a twomicrophone beamformer operating in simulated environments with one interference source and different amounts of reverberation. Compared to a single microphone, beamforming improves the effective target-to-interference ratio by 30, 14, and 0 dB in anechoic, moderate, and severe reverberation. In no case does beamforming lead to worse performance than human binaural listening. Thesis Supervisor: Nathaniel Durlach Title: Senior Scientist __ _ _ _ I_ __ I _ _I I I __ I I _____

Reducing microphone puff noise

Abstract: A low puff boom microphone includes a protective grid covering an end portion of the microphone housing, a microphone capsule near the protective grid, a layer of material between the protective grid and microphone capsule, a spacer between the layer of material, and an open area laterally of the spacer.

Aquatic transducer system

Abstract: An underwater transducer system reproduces high-fidelity audio signals underwater, and detects and monitors low levels of sound activity, both adjacent to a body of water such as a swimming pool, and in the water. The system includes an underwater housing for a diaphragm that directly contacts the water, a coil assembly movable within the housing and rigidly connected to the center of the diaphragm by a tubular member of the coil assembly engaging a cylindrical boss portion of the diaphragm. The housing can be suspended by an elongated cord member from a wall coping, or mounted within a wall fixture structure. The system can have a source of illumination, a conduit from the source terminating in the housing on the coil axis proximate the diaphragm, and an optical element sealingly protrudes the diaphragm for transmitting light-amplified illumination into the water. A head portion of the optical element that substantially fills the boss portion of the diaphragm incorporates a pair of mirrored surfaces for spreading the illumination and transmitting it into the water. A control unit located to one side of the water provides a speaker mode and a microphone mode of operating the transducer, the microphone mode having a monitor mode and an alarm mode for detecting an alarm condition based on discrimination of an alarm sound condition occurring in the pool. The control unit can also interface a closed circuit TV for visually monitoring the pool. Also disclosed is a method for making the underwater transducer.

The acoustic behavior of the fish‐catching bat, Noctilio leporinus, during prey capture

Abstract: Many bats change the acoustic parameters of their echolocation calls in a deliberate manner during prey capture. Attempts to quantify these changes have been either of limited scope or subject to potentially severe errors due to an inadequate consideration of the directionality of both the bat and the recording microphone. Therefore, the echolocation pulses emitted by two N. leporinus have been recorded as they approached and captured stationary prey, with the microphone positioned in such a way that the structure of the pulses incident upon the target could be determined. The results of this study show that: (1) during the last 1.5 m of the approach, N. leporinus reduces the intensity of emitted pulses by 6 dB per halving of distance, so that the intensity incident upon the target is constant; (2) at a point in the pulse train that corresponds to the position of the hypothesized tracking phase of echolocation, N. leporinus selectively reduces the intensity of the frequency‐modulated (FM) fundamental so t...

Variable pattern microphone system

Abstract: A microphone system including a plurality of sound transducers integrally contained in a single microphone housing, wherein each transducer has a different polar pick-up pattern. The system includes a remote combiner for the symmetrical addition of the output of each transducer into a composite signal of variable pattern. In the illustrated implementation, the system includes an electret microphone capsule having an omnidirectional pick-up pattern, an electret microphone capsule having a cardioid pick-up pattern, and an electret microphone capsule having a hypercardioid pick-up pattern. The capsules each have a mechanical acoustic phase shifting element to produce the desired pick-up patterns and are time aligned in the housing by placing the capsules together at the same location while pointing in the same direction. Each capsule has an independent power supply module and adjustable gain amplifier for the acoustical balancing of the system which is also integrally contained in the microphone housing. The combiner is shown implemented as a resistive switching network allowing the selection of multiple patterns, and alternatively, as a number of rheostats connected at a common node thereby providing an infinitely variable selection of patterns.